Growth Analysis of Grain Sorghum as Affected by Planting Density and Amount of Nitrogen

Abstract

This study was conducted to clarify the dry matter production of grain sorghum and growing behavior with relation to planting rate and amount of fertilizer in order to obtain high grain yield. The hybrid variety, GS76Y was seeded on May 24 in 1972. The dry weight of each organ of plant was measured at intervals about 2 weeks apart ranging from the early stages of growth to ripening time. Irrigation was applied at half bloom stage. The results obtained were as follows; 1. The maximum rate of dry matter production was 42 g per m2 of field per day with the high planting density and heavy manuring plot during 14 days near heading date. In this period, mean daily solar radiation was 502 cal per cm2 of field and mean daily temparature was 28.4°C. 2. The mean maximum value of net assimilation rate in heavy manuring plots and in light manuring plots were 17.7 and 14.2 g per m2 of leaf area per day, respectively. The value of net assimilation rate was high at the early stages of plant growth and decreased with grow. 3. Grain yield was significantly varied with the planting density. The highest grain yield per are was 82 kg on the basis of dry matter. lt was obtained at planting densities of 25 and 40 plants per m2 of field on heavy manuring plots. 4. Total dry matter produced in ripening period ranged from 62 to 81 kg per are and was equivalent to above 90 percent of grain yield. 5. Dry matter production was depended largely upon leaf area before heading, and net assimilation rate after heading. The value of net assimilation rate during the ripening period decreased with higher leaf area index. However, in case 4 and beyond that of leaf area index, net assimilation rate was increased as the percent of nitrogen content of leaf blade, namely, there was positive correlation between net assimilation rate and percent of nitrogen content of leaf blade in the ripening period. 6. It was recognized that the number of grains per unit field was closely related to the amount of nitrogen absorption of top at heading date. The amount of nitrogen, phosphorus, and potassium absorption at ripening time were in the range of 17.8 to 25.1, 3 to 4 and 26 to 34 kg per 10 are, respectively.